1. Field of the Invention
The present invention relates to a device and method for performing interbody spinal fusion, stabilization and restoration of the disc height in the spine, and in particular to a device and method for performing percutaneous, minimally invasive interbody fusion of the lumbar spine.
2. Discussion of the Related Art
Many devices exist to assist in maintaining the position of the lumbar vertebra in conjunction with lumbar fusion surgery. Fusion is the joining together of the vertebra of the spine. The underlying concept of the known devices is to maintain the relative position of the vertebral bodies with respect to each other, while the bone that has been placed between the vertebra to form the fusion of the vertebra, has an opportunity to heal and mature. These devices employ different strategies and philosophies, and can include devices which utilize the pedicles, as well as devices which are placed in to the disc space to promote fusion across the disc space. The latter devices and techniques associated with these devices are known as xe2x80x9cinterbody fusionxe2x80x9d. While no single technique has been universally accepted as the most optimum method, there is growing evidence that interbody fusion may be the preferred method.
The interbody fusion procedure may be performed via an anterior or posterior approach. Initially, all interbody fusion procedures were accomplished using the posterior approach. The procedure was performed by first performing a laminectomy, removing the disc space, and then packing the disc space with pieces of bone, which were then permitted to heal over time. The hope was that the inserted bone pieces would grow and fuse together with the vertebra above and below that disc space, forming a bridge of bone between the two vertebral bodies, thus accomplishing the interbody fusion.
Posterior interbody fusion procedures are accomplished via a variety of techniques. Most procedures attempt to restore proper disc height, i.e. the space between the adjacent vertebra. The patient benefits from restoring the proper disc height, particularly where there has been deterioration, degeneration or collapse of the disc.
More recently, the anterior interbody fusion procedure has gained popularity, due to the availability and improvements made in devices that enable the anterior approach for lumbar interbody fusions. These devices typically provide for a retroperitoneal or transperitoneal technique to be used for approaching the lumbar disc, removing some or all of the disc, and placing either bone or a metallic device into the disc space. These devices also typically provide a means for distracting the disc space, i.e. making the space between the discs wider. Presently, this aspect of lumbar interbody fusion procedures are considered to be an important step in the procedure because of its effects on the neural foramina, or areas from which the nerve roots exit through the vertebra. It is generally accepted that enlarging the disc space consequently enlarges the neural foramina, thus decompressing the exiting nerve roots.
The current techniques, due to the present equipment available, particularly for anterior interbody fusion, suffer the disadvantage in that they are major surgeries and require large incisions with the manipulation of both tissue and organs. While attempts have been made to perform anterior interbody fusions laparoscopically, these procedures are often complicated and are typically performed under general anesthesia.
Therefore, a need exists for a method for performing interbody fusions that reduces the trauma to the patient, and consequently reducing recovery time. A device is also needed to facilitate the interbody fusion procedure to enable the procedure to be performed percutaneously, enabling the surgeon to distract the disc to restore disc height, maintain the distraction, and promote the growth of the bone placed in the disc space between the two vertebral bodies, thus accomplishing the interbody fusion.
It is, therefore, an object of the present invention to provide a minimally invasive, percutaneous surgical procedure for performing interbody fusion which reduces the trauma to the patient and reduces recovery time.
It is also an object of the present invention to provide a percutaneous interbody fusion procedure which accomplishes the interbody fusion through small incisions in the body of the patient and utilizes a minimum of incisions to complete the procedure.
It is a further object of the present invention to provide a device which facilitates the percutaneous interbody fusion procedure.
It is yet another object of the present invention to provide a device which distracts the disc space and which may be inserted through a tube to effect the percutaneous interbody fusion procedure.
It is a further object of the present invention to provide a collapsible and expandible interbody fusion spacing device that facilitates the percutaneous interbody fusion procedure.
It is still a further object of the present invention to provide a kit for performing a minimally invasive percutaneous interbody fusion procedure.
The above and other objects of the present invention may be achieved by providing a collapsible and expandible interbody fusion spacer device that may be inserted through a small diameter tube to the disc space that is being fused, so that the procedure may be performed in a minimally invasive manner. The spacer is preferably constructed in two halves that are connected by pins located on the sides of the spacer. The outer surface may be flat to engage the end plate of the vertebra above and below the spacer, and the outer surface may be scored, have ridges, points, tabs, detents, or the like to enhance gripping of the end plates of the vertebra to resist movement of the spacer once it is in place. The interior surfaces of the halves that make up the spacer include a semicircular hollowed portion that is preferably threaded along at least a portion of its length that is aligned with a similar semicircular threaded hollowed portion on the other half of the spacer. When the spacer is assembled, the threaded portion forms a canal for acceptance of a piston screw. Preferably, the threaded canal is tapered from one end to the other, particularly from the end which will be positioned posteriorly in the disc space to the end which will be positioned anteriorly in the disc space. When the piston screw is inserted, the anteriorly positioned end will expand a greater distance in the disc space than the posterior end, due to the tapered threaded canal. This will cause the disc height, i.e. the distance between the vertebra, to be greater anteriorly than posteriorly, which more closely mimics the natural curve of the spine, particularly in the lumbar spine, thus restoring lordosis, the natural curve of the lumbar spine.
A method for performing percutaneous interbody fusion is also provided, in which the disc space is enlarged in the craniocaudal direction following percutaneous discectomy. Following the discectomy, a guide needle is passed through the incision to the disc space between the vertebra. Over the needle, a series of tubularly shaped dilators are passed, with each successive dilator having an inner diameter that is slightly larger than the outer diameter of the dilator that is in place. As each successive dilator is inserted in the disc space, it forces the vertebra apart, increasing the disc space, until a desired height between the vertebra is achieved. Once a desired height is reached, which is only a desired height and not necessarily the maximum height, the outer dilator is left in place, while those inside the outer dilator are removed. The maximum height does not have to be achieved by the dilators because the expandible intervertebral disc spacer of the present invention is then inserted into the disc space through the outer dilator. Once in place, the spacer is expanded to increase the disc height to the maximum distance. After the spacer is in place on one side of the vertebral body, the procedure is repeated on the other side. After the two spacers are in place, a bone matrix, which encourages fusion, is passed through the dilators, filling the space with bone. The dilators are then removed and the procedure is complete.
A kit for performing percutaneous interbody fusion is also provided, which includes a plurality of expandible intervertebral disc spacers, which preferably expand the disc space a greater distance anteriorly than posteriorly, at least one dilator for expanding the disc height and having a hollow interior for allowing passage of the disc spacers to the disc space, and a guide needle. A curette for performing percutaneous discectomies may be provided, and a bone matrix for fusing the vertebra together may also be provided.